Dozens of attackers armed with assault rifles used explosives to blast open the vault of an armored car company in Paraguay early Monday morning and apparently escaped by boat into Brazil with a haul of cash, authorities said.

At least one police officer was killed and three civilians were injured in a blaze of gunfire and torched vehicles during the three-hour attack on the private security company Prosegur in the border city of Ciudad del Este, officials said.

The vault, which can hold up to $40million in cash, 'was full' at the time of the robbery said public prosecutor Denise Duarte.

Guards and police inspect a vault that the assailants blew up early morning in Ciudad del Este, Paraguay, on Monday

Dozens of attackers armed with assault rifles used explosives to blast open the vault of an armored car company early Monday and apparently escaped by boat into Brazil with a haul of cash, authorities said

At least one police officer was killed and three civilians were injured in a blaze of gunfire and torched vehicles during the three-hour attack

The attack was on the private security company Prosegur (pictured above being inspected by policement) in the border city of Ciudad del Este, officials said

It is believed that the thieves took all $40million, but police have not released information to verify the exact amount.

Up to 80 people may have been involved in the attack, said Arsenio Correa, investigations chief in the city.

'The criminals used snipers to guarantee the escape and torched more than 10 vehicles to distract the police,' he said.

Witnesses claimed to hear Portuguese being spoken during the heist, which rose suspicions that the thieves had come across the border from neighboring Brazil, according to The Telegraph.

Up to 80 people may have been involved in the attack, which saw gunfire and cars set on fire for hours

Police said that the robbers set at least ten cars on fire to distract police from the heist on the vault

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A tweet from the ministry showed a photograph of a policeman standing over a body of a man in bloodied camouflage clothing.

A joint Paraguayan-Brazilian police operation against the fleeing assailants led to three suspects being killed and 'at least four arrests'. Pictured above, a bulletproof vest seized by police sitting in a bloodied police vehicle

Witnesses claimed to hear Portuguese being spoken during the heist, which rose suspicions that the thieves had come across the border from neighboring Brazil